1. Field of the Invention
The present invention relates to an off-line diagnosis system in a process control system comprising a host application and field instruments that perform digital communication with the application.
2. Description of the Prior Art
In the prior Japanese patent application 2002-113820 “Off-line diagnosis system,” the applicant has disclosed technology concerning an off-line diagnosis system in a process control system comprising a host application and field instruments that perform digital communication with the application.
FIG. 1 is a function block diagram illustrating the technological details of the prior patent application. Block 1 denotes a field instrument (for example, valve positioner), which communicates with a host system to perform process control (measurement, operation, monitoring, etc.). In block 1, numeral 101 denotes a data transmit means, number 102 denotes a data analyzing means, numeral 103 denotes an input-output characteristics measurement means, and numeral 104 denotes a step response measurement means.
Block 2 denotes a host application that runs on a PC or DCS. In block 2, numeral 201 denotes a data receiving means, numeral 202 denotes a data analyzing means, and numeral 203 denotes a data display means. Numeral 3 denotes a digital 1 communication bus that connects between the data transmit means 101 of the field instrument and the data receiving means 201 of the host application.
Note here that the digital communication mentioned above means communication based, for example, on a communication protocol for the process industry, such as Foundation Fieldbus, PROFIBUS, HART or BRAIN.
Both the data analyzing means 102 and 202 may be provided in either field instrument 1 or host application 2, or may be omitted in cases where the operator himself/herself makes analyses using measured data.
If field instrument 1 is a valve positioner, the input-output characteristics of a control valve or a positioner are measured by input-output characteristics measurement means 103, step responses (response characteristics including those of valves) are measured by step response measurement means 104, and the data thus measured are analyzed by the data analyzing means as necessary and uploaded to the data receiving means 201 of host application 2 through data transmit means 101 and digital communication bus 3.
In host application 2, the measured data or analyzed data that has been received is further analyzed by data analyzing means 202 at higher levels as necessary, and the results of analysis are displayed by data display means 203.
In such a system configuration as described above, assume that the speed of communication between data transmit means 101 and data receiving means 201 is insufficient. Then, in such a type of communication as 1200 bps HART communication, the system would not be considered to have a sufficiently high speed to perform real-time processing, though it can successively receive and display measurement results. Therefore, in order to solve the communication speed problem which causes a bottleneck, a practical system requires data memory means as buffers for temporarily retaining measured data within field instrument 1 and host application 2.
To be specific, the data memory means in this case refers to memory resources. Memory resources are also used for other types of signal processing and, therefore, it is sometimes difficult in terms of cost to secure sufficient memory to store the required data.
On the other hand, in measurement for diagnostic purposes, there is a demand for increasing the number of measurement points as much as possible in order to increase the resolution and thereby ensure measurement accuracy, or for obtaining response characteristics data composed of a plurality of step responses. However, it may not be possible to satisfy such a demand if the capacity of data memory means is insufficient.
An object of the present invention is to provide an off-line diagnosis system whereby the measurement resolution (number of measurement points) can be increased in order to obtain detailed input-output characteristics, and step response characteristics can be obtained at a sufficient frequency and more efficiently, without expanding the physically limited memory capacity of a field instrument or host application.